kellogg



MULTIPLE SW'ITGHBOARD. No. 592,373. Patented 001;. 26, 1897.

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MULTIPLE SWITGHBOARD. No. 592,373. Patented Oct. 26, 1897.

.annunciators.

Ni'rnn STATES PATENT FFICEQ MILO G. KELLOGG, OF CHICAGO, ILLINOIS,ASSIGNOR TO THE KELLOGG SWITCIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

M ULTIPLE SWITCHBOARD.

, SPECIFICATION forming part of Letters Patent No. 592,37 3, datedOctober 26, 1897.

Application filed July 26, 1890. Serial No. 860,083. (No model.)

To on whom it may concern.-

Be it known that I, MILO G. KELLOGG, of Chicago, in the county of Cookand State of Illinois, temporarily residing at Stuttgart, in the Empireof Germany, have invented certain new and useful Improvements inMultiple Switchboards for Telephone-Exchanges, of which the following isa full, clear, concise, and exact description, reference being had tothe accompanying drawings, forming a part of this specification.

My invention relates to the telephone-exchange system described in myapplication, Serial No. 345,065, filed March 24, 1890,(CaseNo. 185.) Insaid application the metallic-circuit lines of the exchange are dividedinto four classes or divisions and theswitchboards of the exchange aredivided into four classes or divisions to correspond. Each line of oneclass is provided with a switch or switch connection on each board ofone class and on one board of each of the other classes. Each line ofthe second, third, and fourth classes is similarly connected to eachboard of its own class and to one board of each of the other classes.For each line there are four polarized Two of the annunciators areconnected in opposite polarity in one of the branches of the line at thecentral office and the other annunciators are connected in oppositepolarity in the circuit of the other branch of the line at the centraloffice. The two branches of the line are normally grounded at thecentral office. .The subscribersstation apparatus is provided with acallinggenerator with commutator-pieces and with calling-keys, wherebythe subscriber may include either branch of his line in a groundcircuitwith his generator and send a current of either polarity to the circuit.

In the invention which I shall now describe each line has four polarizedannunciators, which are connected into the circuit of the two branches,and also a calling-generator and four calling-keys, all connected andoperating substantially as described above for the other application,whereby the subscriber may at will cause either of the four annunciatorsto indicate a call. For each subscriber there is also a privatecalling-wire grounded at the central oflice and with two polarizedannunciators there connected into the circuit, so as to be operated bycurrents of opposite polarity. At the subscribers station there are keysand connections by which the subscriber may at will also operate eitherof these annunciators, so that it indicates a call.

The lines of the exchange are divided into six classes, and theswitchboards of the eX- change are divided into six classes tocorrespond with the six classes of lines. Each line of each class has aswitching connection on each board of its own class and on one board ineach of the other classes. There are switchplugs and connections wherebyan operator at each board may connect togetherinto metalliccircuit'anytwo lines which have switching connections at her board. Thesix annunciators of each line are located in the six sections of boardsand at boards-where the line has switching connections and its calls areintended to be answered. The annunciators and the switches shouldpreferably be distributed among the boards, sothat there are practicallythe same number of annunciators and lines to be answered at each board.

In the accompanying drawings, illustrating my invention, Figure 1represents a complete diagram of the central-oflice main-line apparatus,circuits, and connections of the systern. Fig. 2 shows in detail thecalling-annunciators used at the central office. Fig. 3 shows aretardation-coil to be used for each line. Fig. 4 shows in diagram anoperators cord system or apparatus to be used at the boards. Fig. 5shows in diagram a subscribers'station apparatus to be used at each subscribers station. Fig. 6 shows an end View of the generator-shaft of thesubscribers-station apparatus with two commutator-springs, one bearingon each side of the shaft. Fig. 7 is an end or sectional View of a cablewhich may be used in the exchange system herein described.

G in each case in the drawings represents a ground connection.

In Fig. 1, A A represent sectional views of sections of two switchboardsof one class of boards; B B sectional views of sections of two boards ofanother class; C, of a board of a third class; D, of a board of a fourthclass;

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E, of a board of a fifth class, and F of a board of a sixth class ofboards. The six classes of boards are designated by the letters A, B, O,I), E, and F, respectively, to correspond. Each class of boards willhave as many boards as are necessary in order to carry on successfullythe switching operations required.

For convenience I call one class of lines Class A, a second class, ClassB, a third Class O, a fourth Class D, a fifth Class E, and the sixthClass F of lines. The lines may be each indicated in theexchangecatalogue and elsewhere by the letter or designation of itsclassas, for instance, one line as 32, another 365 a third 365 a fourth4?, a fifth 15 and a sixth C 15F. I

The peculiar designations of the various classes of boards and lines andof the lines in each class are immaterial so long as the division ismade and the distinction kept up.

Each line of one classclass A, for example-has a spring-jack or othersuitable switch on each board of class A of boards andon one board ofeach of the other classes of boards. Each line of. class B may have aswitch on each board of class B and on one board of each of the otherclasses. Each line of class C has aswitchon each board of class C and onone board of each of the other classes. In like manner each line of eachof the other classes of lines has a switch on each board of a separateclass of boards and upon one board in each of the other classes.

In Fig. 1 eight boards are shown, two boards belonging to each ofclasses A and B, and one board belonging to each of the other classes ofboards 0, D, E, and F. Two lines are shown, one line belonging to classA and the other to class B of lines. The calling-annunciatorsof thesetwo lines and their retardation-coils are shown, six annunciators andone retardation-coil for each line. The annunciators of a line aredistributed among the boards, so that one annunciator is at a board ofeach class and where the line has a switch and its calls are to beattended to. The other lines would in like manner have theirannunciators distributed among the several classes of boards.

Each of the switches, as shown, has a contact-spring which normallybears on a contact-point, but is separated from the point while aswitch-plug is inserted into the switch, and has a third or insulatedcontact-piece insulated from the rest except by the circuit connections.This third or insulated contact-piece is placed along the switch-hole,so that a plug can be applied to'it for testing and so that one of thecontact-pieces of, a loop-switch plug inserted into the switch will formconnection with it. The switches are adapted toreceive the loop switchplugs shown in Fig. 4 and when a plug is, in-

sorted into a switch it raises the spring from the contact-point onwhich it normally bears and the two contact-pieces of the plug formconnection with the spring and third or insulated piece of the switch,respectively.

g g are the contact-springs of the switches, h h the contact-points onwhich the springs normally bear, andjj the third or insulatedcontact-pieces of the switches.

a b c are rubber strips, of the shape substantially as shown, onwhichthe metal parts of the switches are mounted and through the fronts of.which are the switch-holes Z Z. These holes are rectilinear and areadapted to receive and guide the switch-plugs and cause them to operatethe switches, as indicated.

The calling-annunciators shown in Fig. 1 and in greater detail in Fig. 2are polarized annunciators of known construction. Each annunciatorresponds or indicates a call when an electric current of one polaritypasses through it, but does not respond when a current of the oppositepolarity passes.

w w are retardation-coils, one'for each line net-circuit made by theiron pieces of the coil.

R is an electric rheotome or circuit-breaker, which may be ofsubstantially the shape shown or of other forms by which an electriccircuit may be alternately made and broken.

In the rheotome shown there may be a gearmovement actuated bya spring,which in its operation alternately makes and breaks the connectionbetween two insulated contactpoints.

The metallic-circuit lines are connected to the central-officeswitchboards and apparatus as follows and as shown for the two linesshown: One side or branch of a line is connected to all thecontact-pieces j j of the switches of the line on the different boards.It afterward passes successively through two of the polarizedannunciators of the line and the retardation -coil of the line and isthen connected to the ground, but not through the rheotomecontact-points. The other side or branch of the line passes normallysuccessively through the several pairs of contacts 9 h of the switchesof the line on the different boards, passing in each case to the spring9 first and then successively through two other of the annunciators ofthe line to one of said insulated contact points of the rheotome. Theother contact-point of the rheotome is connected to, the ground. The twoannunciators in the circuit ofeachof the branches of the line, as abovedescribed, are so connected into the circuit that one is actuated by acurrent of one polarity and the other by a current of the other polaritypassing through them.

Each subscriber has, in addition to his mc tallic-circuit line, aspecial calling wire standard of the frame d.

which is grounded at the central office and has in its circuit theremaining two annunciators of the subscriber. These annunciators arealso so connected that one of them will be operated when a current ofone polarity passes through them and the other will be operated when acurrent of the other polarity passes.

In the operators cord system shown in Fig. :l, D D are apair of doubleor loop-switch plugs adapted to be inserted into the spring-jackswitches of the boards, and when a plug is inserted into a switch itoperates it, as heretofore indicated. The two contact-pieces of eachplug are connected to the other apparatus, as will be described, by thetwo insulated conductors of a double or loop flexible switch-cord. r isthe rubber insulation of the plug, and s s are its two insulatedcontactpieces.

The circuit connections connecting the contact-pieces of the plugs arecontinuous and are flexible throughout their length or to such extent asto permit the required operations.

11 is a switching device for the pair of plugs and cords. This switchingdevice has a rubber frame (markedd) which supports and insulates thevarious parts.

ff are two contact-springs.

1, 2, 3, and at are contact-points located and insulated as shown andwhich form connec tions with the springs f f as will be described.

q is a sliding rod which passes through the It terminates at one end inthe knob e, which is placed in a 0011- venient position for the operatorto manipulate to draw the rod in and out to carry on the switchingoperations, as willbe described.

a 0 p is an irregularly-shaped rubber piece placed at the end of the rodq. The different sections or divisions of this rubber piece are markeda, 0, and p, respectively as indicated.- The rod q carries them in itsreciprocating movement, and altogether they may be called thecommutator-piece of the switching device. All the parts are constructed,insulated, mounted, and adjusted to perform the switching operationswhich I shall describe.

The button 6 and the piece 19 furnish stops for the commutator-piece,which limit its inward and outward motions.

\Vhen the commutator-piece is pushed in until its outer stop is close toor against the standard of the frame (I, the springs f f rest on piece1), and f is in contact with 3, and f is in contact with 1. \Vhen thecommutatorpiece is pulled out into its central position and the springsrest on 0, spring f is out of contact with 1 and 2 and spring f" is incon-- tact with 4. lVhen the commutator-piece is pulled still fartherout and the springs rest on n,f' is in contact with 3 and f is incontact with 2.

t is the operators telephone. S is her calling generator or battery. Sis her test-battery, and it is a resistance-coil.

Each operator has one telephone and resist- 7 is the subscriberstelephone.

ance-eoil and may have one generator and battery.

o is a clearing-out annunciator which may be unpolarized. There is onesuch annunciator for each pair of cords.

The connections of the operators cord system are as follows: The twocontact-pieces s s of the pair of plugs are connected together by meansof a flexible conductor of the pair of cords. The two othercontact-pieces of the plugs s s are connected together by the otherconductor of the cords. The two cordcircuits which connect said pairs ofplug contact-pieces are connected to the contactsprings ff" of theswitching device, spring f being connected withs s,andf with s s. Thecord-circuits which connect .9 s and s 8', respectively, are permanentlycontinuous.

The contact-point. 2 and 3 of the switching device are connectedtogether through the operators telephone and resistance-coil, and 1 and3 are connected together through her calling-generator. The clearing-outannunciator is connected on one side to point 4 and on the other side tothe circuit which connects contacts 5 s. The test-battery is grounded.on one side and connected on the other side to the circuit-wire whichconnects the two telephone-coils.

Each operator has as many pairs of switchplugs and cords with theirswitching devices and clearing-out annunciators as she may need for herwork, and they are connected to her special apparatus substantially asshown and described. Thecords should be long enough so that she canreach any switch at her board, and the apparatus should be suitablymounted for her work. The commutator-piece of each switching deviceshould stand normally, or when it is not in use for switching a pair oflines, in its outer position, so that its springs rest on In thesubscribers-station apparatus shown in Fig. 5, 4 is a telephone-switeh.5 is a'signal-receiving hell. (3 is a calling-generator. 8 8 8 8 9 9 aresix calling-keys, and 10 is a clearing-out switch.

The calling-generator is a usual construction of calling-generatormodified as follows: There is an insulated contact-piece on thearmature-shaft, which is a half-circle and to which one end of thearmature-coil is connected. The remaining part of the circle is aninsulation, as shown. There are two stationary springs which bear ondiametrically opposite parts of that part of the shaft of which theinsulated piece is a part and which in the movement of the armaturealternately make and break connection with said insu- The calling-keys 88 8 8 are three-point keys, having one point on which the keylevernormally bears and another point normally insulated from the lever andwith which the lever comes into contact when it is pressed away from theother point by the subscriber in making a call, as hereinafterdescribed.

The calling-keys 9 9 are two-point keys, having a point normally out ofconnection with the key-lever, but with which the lever comes in contactwhen it is pressed by the subscriber in making a call, as hereinafterindicated.

The clearing-out switch 10 is the usual hand-switch employed to switch atelephone from one circuit to another. It contains a reciprocating blockcarrying three conducting-plates p q u,insulated from one another. Uponplate p normally rest a pair of contact-springs m m, while upon plates qand it rest pairs of contact-springs n n and o 0, respectively. Thereciprocating block, with its parts, is held by a spring normally in theposition shown. When the subscriber presses the block, m m are out ofcontact with plate 19 and are in contact with plates q u, respectively,and said plates q u are out of contact with springs 0 o and are incontact with springs n n, respectively.

The circuits and connectionsof the subscribers-station apparatus aresubstantially as shown and as follows: One side or branch of the line isconnected through the pairs of contact points normally in contact of twoof the keys 8 8, passing in each case to the spring first, and thenpasses through the pairs of contact-points normally in contact of thetwo other keys 8 8, passing in each case with these keys to thecontact-point first. This side thence connects with the other side orbranch of the subscribers line. The line is separated or divided at apoint which is in the circuit while the telephone is on the switch, andthe two ends are connected to the two springs m m, respectively. One ofthe contact-springs which bear, as described, on the armature-shaft isconnected to one of the springs 07/, and the other spring 02 isconnected to the other side of the armature-coil than that towhich theinsulated contact-piece is connected This last spring at bears on'plateq, and the spring 0, which also bears on this plate, is connected to theground. The two keys 8 8 whose connection with the linecir cuit wasfirst described have their lower contact-points (those upon which thelever may be pressed by the subscriber) connected to said twocontact-springs, respectively, of the calling-generator, and the lowercontact-points of the other two keys 8 8 are also connected to saidsprings, respectively. The two levers of the calling-keys 9 9 areconnected to the subscribers end of his special calling-wire, and thetwo contact-points of these keys 9 9 are connected to said twocontact-springs, respectively, of the calling-generator.

It will be seen from the drawings and the description heretofore made ofthe connections and of the apparatus that when the subscriber presses onone of the two keys 8 8, whose connection with the line was firstdescribed and operates his calling-generator one side orbranch of theline is disconnected from the other and has a calling-current of onepolarity sent over it, and that when the other key of the pair isdepressed and the generator operated a current of the other polaritywill go over that branch of the line. The circuit then established isfrom the subscribers ground through the contact established 011 hispressing the key to the branch v of the line connected to the key-leverand through the circuit of that branch to its ground connection at thecentral otlice heretofore described. The subscriber can thereforeoperate (or cause to indicate) at will either of the two polarizedannunciators connected into this branch. In like manner can thesubscriber by operating his calling-generator and pressing on one or theother of his two other keys 8 8 operate at will either of the twoannunciators connected into the circuit with the other branch of theline. By pressing on the lever of one of the keys 9 and operating hisgenerator he can send a current of one polarity through the specialcallingwire, and by pressing on the other key 9 and operating hisgenerator he can send a current of the other polaritythrough the specialcalling-wire. He can therefore at will operate either of theannunciators connected in circuit with his special calling-wire. Thecircuit then established is from the ground through the generator andthe contact established on pressing the key to the calling-wire andthrough its circuit to its ground connection at the central office. Anysubscriber can therefore at will cause any of hissix annunciators at thecentral office to indicate a call.

I prefer to mark or designate the six calling-keys at asubscribers'station A, B, C, D,

E, and F, respectively, to correspond with the six classes of boards atwhich his six calling-annunciators are respectively located.

The operation of the system is as follows: \Vhen a subscriber wants toconverse with any other, he finds in the exchange list or catalogue thenumber and designation of the line wanted. He then presses on the keycorresponding with the designation or class of the line wanted andoperates his callinggenerator. For instance, if the line wan ted belongsto class A he presses on key A, or if to class B he presses on key B,&c. He thereby calls an operator located at a board where he and thesubscriber wanted each has a line-switch. The operator on observing theindication places one plug of a pair of her switch-plugs in thesubscribers switch, and her telephone is thereby included in a closedcircuit with his line and she finds out by conversation what line iswanted. The circuit is complete by the pair of cords used, the

contact-springs ff connected to its flexible conductors andcontact-pieces 3 2, which are connected to the two sides of hertelephone. \Vhen she finds out what line is wan ted, she places acontact-piece of the other plug of the pair on the third or insulatedcontact-piece of the switch of the line wanted. If the line tested isnot switched at any board, a testcireuit is complete from the groundthrough the test-battery and operators telephone to the line, throughthe circuit of the line and the pairs of contact-points of its switcheson the several boards, and thence to ground through the rheotoine. Theoperator will then distinguish in her telephone the make and break of arheotome in the circuit and will therefore know that the line is notswitched at any board. She then places the plug in the switch of theline tested, and both lines (then disconnected from their groundconnection through the rheotome) are connected into a metallic circuit,and this circuit is bridged at the central office by a circuitconnection which contains the operators telephone and resistance-coil.She then pushes the commutator-piece of the switching device of the pairof cords so that the springs rest on piece and spring f is still incontact with piece 3 and f is in contact with 1. A bridge to themetallic circuit is thereby established which contains thecalling-generator and a calling-current will pass in split circuit tothe two lines and operate the signalbell of the subscriber wanted. Theoperator then pulls the commutator-piece out, so that the springs reston o, and the two lines are in a metallic circuit which is bridged orcrossconneoted by the clearing-out annunciator, while neither thetelephone nor the callinggenerator is connected to their circuit. Theconnection with the annunciator is made by the closing of connectionbetween f and 4 and the circuit connections, as described.

If at any time the operator desires to listen to the circuit of thelines to determine whether conversation is finished, she pulls thecommutator-piece of the switching device, so that the springs rest on 2and 3. The metallic circuit is thus bridged by her telephone andresistance-coil, and she can hear any conversation which is passing overthe circuit. The resistance-coil prevents an undue amount oftelephone-current from passing over her telephone-circuit when thecommutator-piece is in the situationdescribed.

If when the test was made,as described,the line had been switched at anyboard, the circuit of the line at the rheotome would have been open atthe pair of contactpoints of the switch used in switching and theoperator would not distinguish the make and break of the rheotome andwould thereby know that the line was already switched for use. i

The operator at any board can only test the lines of the exchange whichhave switches located at her board. She will have no occasion to testany of the other lines.

When the subscribers are through conversation, either one can press onhis clearingout switch and at the same time operate hiscalling-generator. By such operations the subscribers generator isdisconnected from its ground connection and is looped into the circuitof the two lines, and a calling-circuit will go through the circuit andwill operate the clearing-out annunciator which is in it. The operatorwho made the connection will thereby know that the subscribers wish tobe disconnected or cleared out.

It will be observed that when the subscribers are connected together, asdescribed, and the position of the commutator-piece of the switchingdevice of the pair of cords is such that the openings f f rest on 0, themetallic circuit of the two lines is bridged or cross connected at thecentral oiiiee by a circuit which contains the clearing-out annunciatorof the pair of cords. The clearing-out annunciators should preferably beof high re sistance and such as to afford considerable retardation tothe passage of telephone-eurrents It will also be observed that when thecommutator-piece is in one of its other two positions the metalliccircuit is bridged or cross connected by the operators telephone, andwhen it is in its third position the circuit is bridged by thegenerator.

It will be observed that when the two lines are connected together forconversation their circuit is grounded at the central oliice throughpart of their annunciators and their retardation-coils. Theretardation-coils prevent or minimize the effect on the circuit whichmight arise from other metallic circuits connected in like manner to theground. The annunciators themselves offer a retardation to any sucheffect, and the use, size, and construction of the specialretardation-coils will depend on the construction and conditions of theother apparatus and circuits of the exchange. The retardation-coils alsoprovide a resistance which will decrease the amount of calling-currentpassing through the annunciators connected with them when theclearing-out signal is sent in.

In metallic-circuit exchanges of large size the lines will generally bein cables. The special calling-wires, which I have described as a partof the system, may be copper wires of small diameter. There is no otherapparatus than the subscribers generators and the calling-annunciatorsto operate in circuit with them, and it is not material to have theresistance small. In the system shown and described there is but onestrand or wire for the calling wire for each subscriber, and there aretwo insulated strands or wires for his metallic circuit. In the cablesused in this system I plan to use copper wires of small diameter for thecalling-wires, each placed in a space or angle formed in laying up theinsulated metallic-circuit conductors in the usual way, so that eachcalling-wire will be in a separate angle or space between the insulatedconductors and said wires will be insulated and held apart by saidinsulated conductors. No other insulation in the cable need be providedfor the calling-wires and they need not increase the size and will notgreatly increase the cost of the cables. Fig.

-7 shows an end or sectional view of a cable such as I have described.

More than one calling-wire may be used for each line of the exchange,each connected as described and provided with calling -keys andannunciators, as described for the calling-wires. In this way thesubscribers may be provided with a greater number of annunciators thanthe six shown and described, and the lines and the switchboards may bedivided into a greater number of classes to correspond and connectedsubstantially as indicated, with one connection for each line on eachboard of its class and on one board of each of the other classes, and atboards where the line has annunciators.

It is also evident that one of the six callingannunciators shown foreach line may be left out of its circuit and the lines and boards may bedivided into five sections or classes, with a switch for each line oneach board of its class and on one board of each of the other classesand an annunciator for each line placed at a board of each class andwhere the line has a switch. Other annunciators for the several linesmay in like manner be left out of the respective circuits, and a lessnumber of divisions or classes of lines and boards made to correspond.

I use the terms bridge and cross-connect in connection with a completemetallic circuit to describe a connection between one side or branch ofa circuit and its other side orbranch, and an instrumentin a bridge orcross-connecting circuit to the metallic circuit is not in the directcircuit, but is in a circuit connection across the two sides or branchesof the metallic circuit.

I claim as my invention and desire to secure by Letters Patent 1. In atelephone-exchange system, the combination of metallic-circuit linesdivided into six classes, the switchboards divided into six classes, oneclass of boards for each class of lines, each line having a switch oneach board of its class and on one board of each of the other classes,and each branch of each line being normally grounded at the centraloflice, six polarized annunciators for each line, one being located ineach class of boards and at a board where the line has a switch, twobeing connected in opposite polarity in one branch of the line, twoothers being connected in opposite polarity in the other branch of theline and the other two being connected in opposite polarity in a specialcalling-wi re for the line, electric calling apparatus and keys orswitches at each subscribers station whereby the subscriber may at willsend a current of either polarity into a circuit from the ground througheither branch of his line or his special callingwire to the officeground, and switch-connecting apparatus whereby the operator at anyboard may connect together any two lines which have their switches atthe board substantially as set forth.

2. In a telephone-exchange system, the combination of metallic-circuittelephonelines divided into five classes, switchboards divided into fiveclasses, one class of boards for each class of lines, switches for saidlines, one switch for each line on each board of its class and on oneboard of each of the other polarity from his ground through either sideor branch of his line to its central-office ground or may send acalling-current through his special calling-wire, and connectingapparatus whereby the operator at any board may connect together any twolines which have I their switches at her board, substantially as setforth.

3. In a telephone-exchange system, the combination of metallic-circuitlines divided into five classes, switchboards divided into I fiveclasses, one class of boards for each class V of lines, switches forsaid lines, one switch for each line on each. board of its class and onone board of each of the other classes, each branch of each line beingnormally grounded at'the central office, two polarized annunciatorsconnected in opposite polarity in one branch of each line, anannunciator connected in the other branch of the line, a specialcalling-wire for each line, two polarized annunciators connected inopposite polarity in said special calling-wire, said five annunciatorsof 3 each line being located in the five classes of j boards at boardswhere the line has switches, electric calling apparatus whereby anysubscriber may send a calling-current of either polarity through eitherthe said first-mentioned branch of his line or his special calling-wire,or send a calling-current through the other branch of his line, andconnecting apparatus whereby the operator at any board may connecttogether any two lines which have their switches at herboard,substantially as set forth.

4. In a telephone-exchange system, the

combination of metallic-circuit lines divided 1 into four classes,switchboards divided into four classes, one class of boards for eachclass of lines, switches for said lines, one switch for v each line oneach board of its class and on one board of each of the other classes,each branch of each line being normally grounded at the central office,a special calling-wire for each line, two polarized annuneiatorsconnected in opposite polarity in one branch of the line, an annunciatorin the other branch of the line, an annunciator in the specialcalling-wire of the line, the four annunciators of the line beinglocated at boards in the four classes of boards and where the line hasswitches,electric calling apparatus whereby the subscriber may send acalling-current of either polarity through said first-mentioned branchof his line and may send a callingcurrent through the other branch ofthe line and through his special calling-wire, and connecting apparatuswhereby the operator at any board may connect together any two lineswhich have their switches at her board, substantially as set forth.

5. In a telephone exchange system, the combination of metallic-circuitlines divided into four classes, switchboards divided into four classes,one class of boards for each class of lines, switches for said lines,one switch for each line on each board of its class and on one board ofeach of the other classes, each branch of each line being normallygrounded at the central office, a special calling-wire for each line,two polarized annunciators connected in opposite polarity in the specialcalling-wire, and an annunciator in each branch of the line, the fourannunciators of a line being located at boards in the four classes ofboards, and where the line has switches, and electric calling apparatuswhereby the subscriber may send a calling-current of either polaritythrough his special calling-wire or a calling-current through eachbranch of his line, and connecting apparatus whereby the operator ateither board may connect together any two lines which have theirswitches at her board, substantially as set forth.

6. In a telephone exchange system, the combination of metallic-circuitlines divided into three classes, switchboards divided into threeclasses, one class of boards for each class of lines, switches for saidlines, one switch for each line on each board of its class and on oneboard of each of the other classes, a special calling-wire for eachline, an annunciator in each branch of the line, an annunciator in thespecial calling-wire of the line, the three annunciators of the linebeing located in the three classes of boards and where the line hasswitches, electric calling apparatus whereby the subscriber may send acalling-current through either branch of his line and through hisspecial calling-wire, and connecting apparatus whereby the operator atany board may connect together any two lines which have their switchesat her board, substantially as set forth.

7. In a subscribers-station apparatus, four calling-keys normally in thecircuit of his inetallic-circuit line, a calling-generator havingcommutator parts and connections for taking currents of either polarityand circuits and connections whereby the subscriber may on operating hisgenerator and pressing on one and another of his calling-keys disconnectthe two branches of his line from each other and send through each acurrent of either polarity, substantially as set forth.

8. In a telephone-exchange system, a metallic-circuit line, and fourcalling-keys at the subscribers station, each havinga lever normally incontact with a point and another point with which the lever comes incontact when it is pressed by the subscriber away from its other point,said line passing successively through the contacts of the keys normallyin contact passing in two of the keys to the levers first and in theother two keys to the points first, in combination with amagneto-generator having a commutator-piece and two commutator-springsfor taking cnrrents of the two polarities, the two commutator springsbeing connected to the two points respectively not in normal contactwith the levers of the first-mentioned keys and also to the similarpoints respectively of the other two keys, said commutator-pieces beingconnected to one end of the armaturecoil and the other end of the coilbeing connected to the ground, substantially as set forth.

9. In a telephone -exchange system, the combination of the lines dividedinto six classes,the switchboards for said lines divided into sixclasses, one class of boards for each class of lines, switches for saidlines, one switch for each line on each board of its-class and on oneboard of each of the five other classes, signaling apparatus for eachline giving at the will of the subscriber six indications, one at aboard in each of the classes of boards and where his line has a switch,and connecting apparatus at each board whereby an operator at the boardmay connect together any two lines which have their switches at herboard, substantially as set forth.

10. In a telephone-exchange system, the combination of the lines dividedinto five classes, switchboards for said lines divided into fiveclasses, one class of boards for each class of lines, switches for saidlines, one switch for each line 011 each board of its class and on oneboard of each of the four other classes, signaling apparatus for eachline giving at the will of the subscriber five indications, one at aboard in each of the classes of boards and where his line has a switch,and connecting apparatus at each board whereby an operator at the boardmay connect together any two lines which have their switches at herboard, substantially as set forth.

11. In a switching device, two circuitchanging springs f, f, placedcentrally, the outer points 1, 4E, and the inner points 2, 3, all in thesame plane and insulated from one another, in combination with thecommutator-piece 72 0, p, provided with commutatorsurfaces in differentplanes, against which the springs f, f, alternately press as thecommutator-piece is moved to its different positions there being threesurfaces against which spring f alternately presses, each of which isfarther than the other from the center of the com1nutator-piece in itsline of motion, there also being three surfaces against which spring falternately presses, the middle surface being farther from such centerof the commutator-piece, and the two other surfaces being in the sameplane with each other, whereby in the first position of thecommutator-piece springs f f are in contact with the points 2 and 3,respectively, in the second position of the commutator-piece, f is incontact with 4 and f out of contact with 2, and in the third position ofthe co1ninutator-piece,f,f, are in 15 contact with 1 and 3,respectively, substantially as set forth.

In Witness whereof I hereunto subscribe my name this 23d day of June,1890.

MILO G. KELLOGG.

Witnesses:

EMIL ABENHEIM, (J. STRIoH-CHAPELL.

